<template>
    <ul class="list">
        <li
          class="item"
          v-for="item of letters"
          :key="item"
          :ref="item"
          @touchstart.prevent="handleTouchStart"
          @touchmove="handleTouchmove"
          @touchend="handleTouchend"
          @click="handleLetterClick">
          {{item}}
        </li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    data () {
        return {
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    computed: {
        letters () {
            return Object.keys(this.cities)
        }
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart (e) {
            this.touchStatus = true
        },
        handleTouchmove (e) {
            if (this.touchStatus) {
                let that = this
                if (this.timer) { clearTimeout(this.timer) }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - that.startY) / 20)
                    if (index >= 0 && index < that.letters.length) {
                        that.$emit('change', that.letters[index])
                    }
                }, 16)
            }
        },
        handleTouchend (e) {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
  display: flex
  flex-direction: column
  justify-content: center
  position: absolute
  top: 1.58rem
  right: 0
  bottom: 0
  width: .4rem
  .item
    line-height: .4rem
    text-align: center
    color: $bgColor
</style>
